Negative electrode sheet and use thereof

Abstract

The present application provides a negative electrode sheet and the use thereof. The negative electrode sheet of the present application comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector. The negative electrode active material layer comprises a hard carbon material and a nano-scale lubrication factor, wherein the nano-scale lubrication factor comprises a mixture of a nano-oxide and a nano-sulfide at a mass ratio of (1-3):1, the nano-oxide being selected from SiO2 and / or Al2O3, and the nano-sulfide being selected from MoS2. By introducing the nano-scale lubrication factor into the hard-carbon negative electrode active material layer, the negative electrode sheet has a high compaction density, a low electrolyte weight-cell capacity ratio, and low electrode sheet resistivity.

Description

A negative electrode sheet and application thereof

[0001] The present application claims priority to the Chinese patent application No. 202411067897.X, filed on August 6, 2024, and entitled "A negative electrode sheet and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a negative electrode sheet and application thereof. BACKGROUND

[0003] Lithium-ion batteries (LIBs) have been widely used in power batteries, consumer electronics, energy storage and other fields due to their high energy density, long cycle life and mature industrial manufacturing. However, the low reserves and uneven distribution of lithium resources hinder the sustainable development of LIBs, so it is urgent to develop new energy storage technologies to replace LIBs in some fields. Sodium, as an alkali metal element adjacent to lithium in the periodic table, has similar physicochemical properties. Therefore, sodium-ion batteries (SIBs) have attracted widespread attention as potential alternatives to LIBs due to the wide availability and low cost of sodium precursors.

[0004] Currently, the negative electrode materials of sodium-ion batteries mainly include tin-based materials, antimony-based materials, silicon-based materials, soft carbon materials, sodium ion conductors, and hard carbon materials. Among the many negative electrode materials, hard carbon materials are considered the most likely to be the first to realize industrialization of secondary battery negative electrode materials due to their low cost, good electrical conductivity, environmental friendliness, and abundant sources.

[0005] However, hard carbon negative electrode materials have high mechanical strength and many angular particles, which leads to low compaction density of the negative electrode sheet during rolling, resulting in low volumetric energy density of the negative electrode sheet and high liquid injection coefficient, significantly slowing down the application and development of sodium-ion batteries. SUMMARY

[0006] The present application provides a negative electrode sheet, which has high compaction density, low liquid injection coefficient, and low sheet resistivity by introducing a nano-lubricating factor into the hard carbon negative electrode active material layer.

[0007] The present application also provides a battery, which has excellent energy density and high initial efficiency due to the inclusion of the above-mentioned negative electrode sheet.

[0008] The present application also provides an electronic device, which has excellent energy density and high initial efficiency during use due to the inclusion of the above-mentioned battery.

[0009] The first aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a hard carbon material and a nano-lubricating factor.

[0010] The nano-lubricating factor comprises a mixture of nano-oxide and nano-sulfide with a mass ratio of (1-3):1.

[0011] The nano-oxide is selected from SiO2 and / or Al2O3, and the nano-sulfide is selected from MoS2.

[0012] The negative electrode sheet as described above, wherein the D50 particle size of the nano-lubricating factor is 50-800 nm.

[0013] The negative electrode sheet as described above, wherein the D50 particle size of the hard carbon material is 3-10 μm.

[0014] The negative electrode sheet as described above, wherein the mass ratio of the hard carbon material to the nano-lubricating factor is 100:(0.1-10).

[0015] The negative electrode sheet as described above, wherein the negative electrode active material layer further comprises a conductive agent and / or a binder.

[0016] The mass ratio of the hard carbon material, the nano-lubricating factor, the conductive agent and the binder is (80-100):(1-5):(0-5):(0.1-10).

[0017] The negative electrode sheet as described above, wherein the compaction density of the negative electrode sheet is ≥0.98 g / cm 3 , the resistivity is 0.2-0.8 mΩ·cm, and the porosity is 30%-40%.

[0018] The second aspect of the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises the negative electrode sheet of the first aspect.

[0019] The battery as described above, wherein the electrolyte comprises 5%-20% of NaPF6, 30%-60% of propylene carbonate, 30%-50% of ethyl methyl carbonate, 2%-5% of fluoroethylene carbonate, 0.1%-0.8% of propylene-1,3-sulfonyl lactone and 0.2%-0.8% of ethylene sulfate in terms of mass percentage.

[0020] The battery as described above, wherein the electrolyte has an injection coefficient of 3-10 g / Ah.

[0021] The test method of the injection coefficient is as follows: taking a fresh battery cell and weighing it to be total weight g1, after disassembling the battery cell, weighing the dry electrode sheet to be g2, weighing the structure to be g3, obtaining the injection amount g = g1-g2-g3; then calculating the injection coefficient by injection amount / battery cell capacity, unit g / Ah.

[0022] The third aspect of the application provides an electronic device comprising the battery of the second aspect.

[0023] The implementation of the application has at least the following beneficial effects:

[0024] 1) The application introduces a nano-lubricating factor into the hard carbon negative electrode based on the "ball" action mechanism in nanotribology. The nano-lubricating factor can play the role of a micro ball bearing between hard carbon particles. Under heavy load, the nano-lubricating factor is flattened, which can fill and improve the surface roughness of the hard carbon surface, reduce the friction resistance, reduce the friction coefficient, and improve the compaction density of the negative electrode sheet.

[0025] 2) The nano-lubricating factor has high surface energy and can be fully adsorbed and wrapped on the surface of the hard carbon particles, improving the compression resistance of the hard carbon material, so that it is not easy to crack and break under high rolling load.

[0026] 3) The nano-lubricating factor of the application can replace part of the conductive agent. While improving the pressure density and battery energy density, the contact resistance between hard carbon particles is reduced, which has no negative effect on the electronic transmission performance and even has a certain degree of improvement, so that the first circle coulomb efficiency of the battery and the peel strength of the electrode sheet are improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the distribution of hard carbon material and nano-lubricating factor in the negative electrode sheet of the application and a partial enlarged view;

[0028] Figure 2 is an SEM image of the cross section of the negative electrode sheet of Example 1 of the application;

[0029] Figure 3 is an SEM image of the cross section of the negative electrode sheet of Example 2 of the application;

[0030] Figure 4 is an SEM image of the cross section of the negative electrode sheet of Example 3 of the application;

[0031] Figure 5 is an SEM schematic diagram of the cross section of the negative electrode sheet of Comparative Example 1 of the application.

[0032] Explanation of reference signs: 1-hard carbon particles; 2-nano-lubricating factor. DETAILED DESCRIPTION

[0033] In order to make the purposes, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0034] The hard carbon negative electrode material has high mechanical strength, many particle edges and corners and a multi-pore structure. In the rolling process of the hard carbon negative electrode, the particles are difficult to slide and fill the micropores, resulting in high porosity of the negative electrode sheet. Meanwhile, the hard carbon material has high disorder degree, and the stacking and cross-linking of carbon layers in the microstructure result in large elastic strain and large rebound, so that the compaction density is also low during rolling, resulting in low volumetric energy density of the battery and high liquid injection coefficient.

[0035] Based on this, the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a hard carbon material and a nano-lubricating factor;

[0036] The nano-lubricating factor comprises a mixture of nano-oxides and nano-sulfides in a mass ratio of (1-3):1.

[0037] The nano-oxides are selected from SiO2 and / or Al2O3, and the nano-sulfides are selected from MoS2.

[0038] Figure 1 in the present application is a distribution diagram and a local enlarged view of the hard carbon material and the nano-lubricating factor in the negative electrode sheet of the present application. As shown in Figure 1, the nano-lubricating factor 2 in the present application is fully adsorbed on the surface of the hard carbon particles 1 and fills the gaps between the hard carbon particles 1, playing a lubricating role, reducing the friction coefficient between the hard carbon particles, increasing the sliding and rolling friction, so that the hard carbon particles fully slide and fill the micropores under the rolling stress, reducing the gap between the particles and increasing the contact area between the particles, reducing the porosity of the negative electrode sheet, increasing the compaction density and reducing the liquid injection coefficient. In addition, due to the closer contact between the particles, the contact resistance is reduced, the electronic transmission capacity is not significantly reduced but even improved, so that the negative electrode sheet has a lower resistivity, and the first cycle coulombic efficiency of the battery is improved.

[0039] When the particle size of the nano-lubricating factor is too large, it is not easy to be adsorbed and filled in the surface of the hard carbon particles and micropores; when the particle size of the nano-lubricating factor is too small, the dispersion of the particles is poor, and secondary particles are easily formed, which also leads to the difficulty in uniform dispersion and wrapping in the surface of the hard carbon particles and micropores, resulting in poor lubrication effect. In a specific embodiment, the D50 particle size of the nano-lubricating factor is 50-800 nm, preferably 200-400 nm. Within the above particle size range, the nano-lubricating factor is more easily adsorbed on the surface of the hard carbon particles and filled in the micropores of the hard carbon particles, further improving the compaction density.

[0040] For example, the D50 particle size of the nano-lubricating factor can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, or a range formed by any two of them.

[0041] In a specific embodiment, the D50 particle size of the hard carbon material is 3-10 μm. By using a hard carbon material with the above particle size range, a synergistic effect of particle packing and pore filling can be formed between the nano-scale nano-lubricating factor which is much smaller than the pore (micron level), so that the nano-lubricating factor is fully filled into the pores between the hard carbon particles, plays the role of a micro ball bearing, and under heavy load rolling, fills and improves the surface roughness of the hard carbon surface, reduces the friction resistance, and reduces the friction coefficient.

[0042] In a specific embodiment, the nano-oxide includes one or more of SiO2, Al2O3, TiO2;

[0043] And / or, the nano-polymer includes one or more of polystyrene, polymethyl methacrylate;

[0044] And / or, the nano-carbon material includes one or more of fullerene C60, diamond, graphene;

[0045] And / or, the nano-boron compound includes one or more of calcium borate, magnesium borate;

[0046] And / or, the nano-sulfide includes one or more of ZnS, MoS2;

[0047] And / or, the nano-metallic element includes one or more of Cu, Al, Zn.

[0048] The inventors have found that when the nano-lubricating factor comprises a mixture of nano-oxide and nano-sulfide in a mass ratio of (1-3):1, and the nano-oxide is further selected from SiO2 and / or Al2O3, and the nano-sulfide is further selected from MoS2, the negative electrode sheet has a higher compaction density and a lower resistivity. The reason is that MoS2 has a sheet structure, and the intermolecular bonding force is very weak, and the layer-to-layer slip occurs under a very small shear force, thereby increasing the sliding friction between the hard carbon, reducing the friction coefficient and the friction force; the spherical SiO2 and / or Al2O3 particles can act as micro ball bearings, and under the action of heavy load, the nano-lubricating factor is flattened, which can fill and improve the surface roughness of the hard carbon surface, reduce the friction resistance, and reduce the friction coefficient. When the two are mixed in the above mass ratio range, in addition to their own lubricating effect on the hard carbon, they can also play a synergistic effect, the spherical SiO2 and / or Al2O3 particles can promote the intermolecular slip of MoS2, increase the overall sliding friction, and at the same time, the spherical SiO2 and / or Al2O3 particles have a smaller slip surface due to the more friction coefficient of MoS2, and the rolling friction is also increased, therefore, the combination of the two can make the negative electrode sheet have a higher compaction density.

[0049] The source of the hard carbon material is not particularly limited in the present application, and it can be obtained by commercial purchase or self-preparation.

[0050] In a specific embodiment, the hard carbon material is obtained by carbonization of one or more of needle coke, pitch tar, petroleum coke, isophthalic coke, starch, coconut shell, walnut shell, olive shell, oil tea shell, oil tung shell, chestnut shell, phenolic resin, epoxy resin, urea-formaldehyde resin, straw, and wood.

[0051] Further, the carbonization temperature can be 1000-1600°C. In order to obtain a granular hard carbon material, after carbonization, it can also be subjected to a crushing treatment.

[0052] In a preferred embodiment, the mass ratio of the hard carbon material to the nano-lubricating factor is 100:(0.1-10), and more preferably, the mass ratio of the hard carbon material to the nano-lubricating factor is 100:(0.5-6). Within the above mass ratio range, the nano-lubricating factor can fully play a lubricating role, and the decrease of the amount of active material in the negative electrode sheet caused by the excessive addition of the nano-lubricating factor can be avoided, thereby reducing the battery energy density.

[0053] In a specific embodiment, the negative electrode active material layer further comprises a conductive agent and / or a binder, wherein the mass ratio of the hard carbon material, the nano-lubricating factor, the conductive agent, and the binder is (80-100):(1-5):(0-5):(0.1-10).

[0054] The inventors have found that even if the nano-lubricating factor is used to replace part of the conductive agent within the above range, the electrochemical performance of the battery will not be significantly affected. Therefore, the negative electrode sheet of the present application can also reduce the manufacturing cost of the negative electrode sheet.

[0055] The type of conductive agent is not particularly limited in the present application, and it can be selected from the conductive agents commonly used in the art, including but not limited to one or more of acetylene black, Super P, Super S, carbon fiber, carbon nanotube, and Ketjen black.

[0056] The type of binder is also not particularly limited in the present application, and it can be selected from the binders commonly used in the art, including but not limited to one or more of polyvinylidene fluoride (PVDF), vinylidene-hexafluoropropylene copolymer, polytetrafluoroethylene, polyacrylonitrile, polypropylene carbonate, styrene butadiene rubber (SBR), nitrile rubber, sodium carboxymethyl cellulose (CMC-Na), polyethylene oxide, and ethylene oxide-propylene oxide copolymer.

[0057] The composition of the negative electrode current collector is not particularly limited in the present application, and it can be selected from the negative electrode current collectors commonly used in the art, such as copper foil.

[0058] Further, by controlling the type, particle size, mixing ratio, and other factors of the above nano-lubricating factor and hard carbon material, the compaction density of the negative electrode sheet can be ≥0.98 g / cm 3 , the resistivity is 0.2-0.8 mΩ·cm, and the porosity is 30%-40%, thereby making the battery have high energy density, high initial efficiency, and low liquid injection coefficient.

[0059] The negative electrode sheet of the present application can be prepared by referring to conventional methods, for example, in one specific embodiment, the negative electrode sheet can be prepared by referring to the following method:

[0060] The hard carbon material, nano-lubricating factor, conductive agent, and binder are mixed according to the designed mass ratio to form a slurry, and then the slurry is sequentially subjected to coating, drying, rolling, and sheet making processes to obtain the negative electrode sheet.

[0061] Preferably, the viscosity of the slurry is 2000-8000 mPa·S.

[0062] Preferably, the drying temperature is 60-120°C, and the drying time is 20 min-60 min.

[0063] The present application also provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the negative electrode sheet comprises the above negative electrode sheet.

[0064] The battery of the present application has high energy density, high initial efficiency, and low liquid injection coefficient due to the inclusion of the above negative electrode sheet.

[0065] The battery of the present application can be a lithium ion battery or a sodium ion battery, preferably a sodium ion battery.

[0066] In a preferred embodiment, the electrolyte of the present application comprises 5-20% of NaPF6, 30-60% of propylene carbonate (PP), 30-50% of ethyl methyl carbonate (EMC), 2-5% of fluoroethylene carbonate (FEC), 0.1-0.8% of propylene-1,3-sulfone acid lactone (PST), and 0.2-0.8% of vinyl sulfate (DTD) by mass percentage.

[0067] Further, the present application can make the injection coefficient of the electrolyte reach 3-10 g / Ah by controlling the composition of the electrolyte and the negative electrode sheet.

[0068] The test method of the injection coefficient is as follows: taking a fresh battery cell and weighing it as the total weight g1, disassembling the battery cell, weighing the dry electrode sheet as g2, weighing the structural part as g3, obtaining the injection amount g = g1-g2-g3; then calculating the injection coefficient by the injection amount / battery capacity, unit g / Ah.

[0069] The present application does not particularly limit the composition of the positive electrode sheet, which can refer to the conventional positive electrode sheet composition in the art. Specifically, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector.

[0070] The present application does not particularly limit the composition of the positive electrode current collector, which can be selected from the conventional positive electrode current collector used in the art, such as aluminum foil.

[0071] In a specific embodiment, the positive electrode active material layer comprises a positive electrode active material, a conductive agent, and a binder.

[0072] Specifically, the positive electrode active material includes but is not limited to one or more of a layered metal oxide, a polyanion compound, and a Prussian blue / white compound.

[0073] The types of the conductive agent and the binder can refer to the selection range of the conductive agent and the binder in the negative electrode sheet, which will not be repeated here.

[0074] The composition of the separator can also refer to the conventional separator composition in the art, for example, the separator can be a PP separator, a PE separator, a PP and PE composite separator, etc.

[0075] The present application does not particularly limit the preparation method of the battery, which can be prepared by referring to the conventional method in the art.

[0076] For example, in a specific embodiment, the battery can be prepared by the following steps:

[0077] The positive electrode sheet, the separator and the negative electrode sheet are sequentially placed, and then a battery cell assembly is obtained by winding or stacking, and then a battery is obtained after treatment such as liquid injection, formation, and capacity grading.

[0078] The application also provides an electronic device comprising the battery as above. The electronic device is not particularly limited in the application, and can be any power consumption device comprising the battery, including but not limited to a mobile phone, a portable device, a notebook computer, an electric bicycle, an electric vehicle, an electric toy, an energy storage device, etc.

[0079] The negative electrode sheet and its application provided by the application will be specifically introduced below through specific examples.

[0080] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art, and can be obtained by commercial purchase. The reagents involved can also be obtained by conventional methods in the art.

[0081] Example 1

[0082] The application provides a negative electrode sheet and a battery, and the preparation method is as follows:

[0083] 1. Preparation of the negative electrode sheet

[0084] A hard carbon material with a particle size D50 of 6 μm, a nano-lubricating factor SiO2 with a particle size D50 of 300 nm, a conductive agent SP, SBR and CMC-Na are dispersed in water according to a mass ratio of 95:1.5:0.5:1.5:1.5 to form a negative electrode active paste with a viscosity of 3000 mPa·s, and the negative electrode active paste is coated on both sides of the negative electrode current collector 15 μm aluminum foil, baked at 80℃ for 20 min, then rolled, and the sheet is obtained to obtain the negative electrode sheet.

[0085] 2. Preparation of the positive electrode sheet

[0086] The positive electrode active material layered oxide NFM (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2), a conductive agent SP and PVDF are mixed according to a mass ratio of 97:1.5:1.5 to form a slurry, which is then coated on both sides of the positive electrode current collector 17 μm carbon-coated aluminum foil, baked at 80℃ for 20 min, rolled, and the sheet is obtained to obtain the positive electrode sheet.

[0087] 3. Assembly of the battery

[0088] The negative electrode sheet prepared above, the separator and the positive electrode sheet prepared above are sequentially placed, and then a battery cell is obtained by winding. After the battery cell is placed in an outer packaging foil, an electrolyte is injected, and the battery is obtained after treatment such as formation and capacity grading.

[0089] The electrolyte comprises 10% of NaPF6, 50% of PP, 35% of EMC, 4% of FEC, 0.4% of PST, and 0.6% of DTD in terms of mass percentage.

[0090] Embodiment 2

[0091] The embodiment provides a negative electrode sheet and a battery, and a preparation method thereof is basically the same as that in Embodiment 1, except that the mass ratio of the hard carbon material, the conductive agent SP, the nano lubricating factor SiO2, SBR and CMC is replaced by 95:1.0:1.0:1.5:1.5 in the preparation of the negative electrode sheet.

[0092] Embodiment 3

[0093] The embodiment provides a negative electrode sheet and a battery, and a preparation method thereof is basically the same as that in Embodiment 1, except that the conductive agent SP is not added, and the mass ratio of the hard carbon material, the nano lubricating factor SiO2, SBR and CMC is 95:2:1.5:1.5 in the preparation of the negative electrode sheet.

[0094] Embodiment 4

[0095] The embodiment provides a negative electrode sheet and a battery, and a preparation method thereof is basically the same as that in Embodiment 2, except that the nano lubricating factor is replaced by SiO2 and MoS2 with a mass ratio of 3:1 in the preparation of the negative electrode sheet.

[0096] Embodiment 5

[0097] The embodiment provides a negative electrode sheet and a battery, and a preparation method thereof is basically the same as that in Embodiment 2, except that the particle size D50 of the nano lubricating factor used is replaced by 100 nm in the preparation of the negative electrode sheet.

[0098] Embodiment 6

[0099] The embodiment provides a negative electrode sheet and a battery, and a preparation method thereof is basically the same as that in Embodiment 2, except that the particle size D50 of the nano lubricating factor used is replaced by 900 nm in the preparation of the negative electrode sheet.

[0100] Embodiment 7

[0101] The embodiment provides a negative electrode sheet and a battery, and a preparation method thereof is basically the same as that in Embodiment 2, except that the particle size D50 of the hard carbon material used is replaced by 2 microns in the preparation of the negative electrode sheet.

[0102] Embodiment 8

[0103] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the nano lubricating factor is replaced by Al2O3.

[0104] Embodiment 9

[0105] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the nano lubricating factor is replaced by TiO2.

[0106] Embodiment 10

[0107] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the nano lubricating factor is replaced by CaCO3.

[0108] Embodiment 11

[0109] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the nano lubricating factor is replaced by polystyrene microspheres.

[0110] Embodiment 12

[0111] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the nano lubricating factor is replaced by fullerene C60.

[0112] Embodiment 13

[0113] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the nano lubricating factor is replaced by calcium borate.

[0114] Embodiment 14

[0115] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the mass ratio of the hard carbon material, the conductive agent SP, the nano lubricating factor SiO2, SBR and CMC is replaced by 79:1.0:15:1.5:1.5.

[0116] Embodiment 15

[0117] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 1, except that in the preparation of the negative plate, the mass ratio of the hard carbon material, the conductive agent SP, the nano lubricating factor SiO2, SBR and CMC is replaced by 95:1.95:0.05:1.5:1.5.

[0118] Example 16

[0119] This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by Al2O3 and MoS2 with a mass ratio of 3:1.

[0120] Example 17

[0121] This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by MoS2.

[0122] Example 18

[0123] This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by SiO2, Al2O3 and MoS2 with a mass ratio of 1.5:1.5:1.

[0124] Example 19

[0125] This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by TiO2 and MoS2 with a mass ratio of 3:1.

[0126] Example 20

[0127] This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by ZnS.

[0128] Example 21

[0129] This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by SiO2 and ZnS with a mass ratio of 3:1.

[0130] Example 22

[0131] This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by SiO2 and MoS2 with a mass ratio of 1:1.

[0132] Example 23

[0133] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the nano lubricating factor is replaced by SiO2 and MoS2 with a mass ratio of 2:1.

[0134] Embodiment 24

[0135] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the nano lubricating factor is replaced by Cu.

[0136] Embodiment 25

[0137] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the particle size D50 of the hard carbon material used is replaced by 3 mu m.

[0138] Embodiment 26

[0139] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the particle size D50 of the hard carbon material used is replaced by 10 mu m.

[0140] Embodiment 27

[0141] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the particle size D50 of the hard carbon material used is replaced by 12 mu m.

[0142] Embodiment 28

[0143] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the particle size D50 of the nano lubricating factor used is replaced by 600 nm.

[0144] Embodiment 29

[0145] The embodiment provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 2, except that in the preparation of the negative plate, the particle size D50 of the nano lubricating factor used is replaced by 30 nm.

[0146] Comparative Example 1

[0147] The comparative example provides a negative plate and a battery, a preparation method of which is basically the same as that of the embodiment 1, except that in the preparation of the negative plate, no silicon dioxide is added, and the mass ratio of the hard carbon material, the conductive agent SP, SBR and CMC is 95:2:1.5:1.5.

[0148] Comparative Example 2

[0149] The present example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by SiO2 and MoS2 with a mass ratio of 1:3.

[0150] Comparative Example 3

[0151] The present example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 2, except that in the preparation of the negative electrode sheet, the nano-lubricating factor is replaced by SiO2 and MoS2 with a mass ratio of 4:1.

[0152] Test Example

[0153] 1. Cross-sectional SEM

[0154] Test Method: The cross-sectional morphology photos of the negative electrode sheets of Examples 1-3 and Comparative Example 1 were collected by scanning electron microscopy, and the distribution of nano-lubricating factors and pores in the negative electrode sheets was observed.

[0155] Figure 2 is an SEM image of the cross-section of the negative electrode sheet of Example 1, Figure 3 is an SEM image of the cross-section of the negative electrode sheet of Example 2, Figure 4 is an SEM image of the cross-section of the negative electrode sheet of Example 3, and Figure 5 is an SEM image of the cross-section of the negative electrode sheet of Comparative Example 1. As can be seen from the comparison of Figures 2-5, the negative electrode sheet of Comparative Example 1 has many and large pores between the hard carbon particles, a high porosity, and a low compaction density of the electrode sheet, while the negative electrode sheets of Examples 1-3 have gradually smaller gaps between the hard carbon particles, more closely contacted particles, and gradually lower porosity, as the proportion of nano-lubricating factors increases.

[0156] 2. Compaction density of negative electrode sheet

[0157] Test Method: The negative electrode sheets of the examples and comparative examples were gradually pressed under a pressure of 0-50 t, and the thickness of the electrode sheet was measured, then the maximum compaction density that the electrode sheet could reach was determined in combination with the surface state of the electrode sheet, and the value was listed in Table 1.

[0158] 3. Resistivity of negative electrode sheet

[0159] Test Method: The overall resistivity of the negative electrode sheets of the above examples and comparative examples, i.e., the sum of the resistivity of the active material layer, the contact resistivity between the active material layer and the current collector, and the resistivity of the current collector, was directly measured by the double-plane controllable pressure disc electrode resistance method of the BER series multifunctional electrode resistance meter, and the numerical value was listed in Table 1.

[0160] 4. First-cycle coulombic efficiency of battery

[0161] Test method: the lithium ion battery of the example and the comparative example was charged to the upper limit voltage 3.8V at the current density 0.33C in the constant current charging and discharging mode, then charged to the cut-off current 0.05C at 3.8V, then discharged to the cut-off voltage 2.0V at 0.33C, the first circle charging capacity Q1 and the first circle discharging capacity Q2 of the battery were recorded, and the first circle coulomb efficiency of the battery was calculated according to Q2 / Q1. The results are shown in Table 1.

[0162] 5, injection coefficient

[0163] Test method: the weight of the fresh cell was taken as the total weight g1, after the cell was disassembled, the weight of the dry electrode g2 and the weight of the structural member g3 were taken, and the injection amount g = g1-g2-g3 was obtained; then the injection coefficient was calculated by injection amount / cell capacity, and the unit was g / Ah. The results are shown in Table 1.

[0164] 6, porosity of negative electrode sheet

[0165] Test method: the porosity of the negative electrode sheet was tested by the mercury injection method according to GB / T 21650.1-2008 "Mercury injection method and gas adsorption method for determining pore size distribution and porosity of solid materials".

[0166] Table 1

[0167] From Table 1, the following conclusions can be drawn:

[0168] 1) The porosity of the negative electrode sheet, the injection coefficient and the compaction density of the negative electrode sheet are related, the lower the porosity of the negative electrode sheet, the smaller the injection coefficient, and the higher the compaction density of the negative electrode sheet.

[0169] 2) The resistivity of the negative electrode sheet is related to the content of the conductive agent and the nano lubricating factor, the more the content of the nano lubricating factor, the greater the compaction density of the negative electrode sheet, the more closely the hard carbon particles contact, the smaller the contact impedance, and the smaller the resistivity of the negative electrode sheet;

[0170] From the comparison of Examples 1-3 and Examples 14-15, it can be seen that when the nano lubricating factor is a non-conductive particle, with the increase of the content of the nano lubricating factor and the decrease of the content of the conductive agent, the conductivity will be reduced, which is not conducive to the resistivity of the negative electrode sheet; when the content of the conductive agent is fixed and the content of the nano lubricating factor is increased and the content of the hard carbon material is reduced, the resistivity of the negative electrode sheet is increased, and because the excessive nano lubricating factor is difficult to disperse in the negative active material layer, it is difficult to play a lubricating role due to uneven dispersion, which leads to a significant decrease in the compaction density of the negative electrode sheet;

[0171] In summary, multiple factors need to be considered to balance the non-conductive nano-lubricating factor and the amount of conductive agent added so that the negative plate has both high compaction density and low negative plate resistivity;

[0172] As can be seen from the comparison of Examples 2, 12 and 24, when the nano-lubricating factor is conductive fullerene C60 and nano-element Cu, the lubricating effect of the two is weaker than that of silicon dioxide, resulting in higher porosity and lower compaction density of the negative plate, but due to the conductive effect of the nano-lubricating factor, the negative plate still has an electrical resistivity comparable to that of Example 2.

[0173] 3) As can be seen from the comparison of Comparative Examples 1, 2, 3 and 15, as the content of the conductive agent increases, the first-cycle coulombic efficiency of the battery gradually decreases, which is because the conductive agent has a large number of lithium-reactive active sites, which will consume active lithium ions during formation, resulting in a decrease in the first-cycle coulombic efficiency; and as can be seen from the comparison of Example 2 and Example 14, when the content of the conductive agent in the negative active material layer is consistent, excessive increase in the content of the nano-lubricating factor and decrease in the content of the hard carbon material, the first-cycle coulombic efficiency of the battery increases, which is because when the content of the hard carbon material is low, the film-forming active site is also low, so the lithium ion content consumed in the formation of the SEI film during the first charge and discharge is low, which is conducive to the improvement of the first-cycle coulombic efficiency of the battery.

[0174] 4) As can be seen from the comparison of Example 2, 4, 8-13, 16-24, compared with the nano-lubricating factor selected from TiO2, CaCO3, polystyrene microspheres, fullerene C60, calcium borate, MoS2, ZnS and other compounds, the two nano-oxides of silicon dioxide and Al2O3 exhibit better nano-lubricating effect, which can make the negative plate have higher density; and surprisingly, although the use of ZnS and MoS2 alone as nano-sulfides cannot make the negative plate have high compaction density, when a mixture of nano-oxides and nano-sulfides is used as the nano-lubricating factor, the negative plate has high compaction density, all not less than 1.03 g / cm 3 , especially when the nano-lubricating factor is a mixture of SiO2 and MoS2 or a mixture of Al2O3 and MoS2, and the mass ratio of the two is 3:1, the compaction density of the negative plate is the highest, and the negative plate also has low resistivity and high first-cycle coulombic efficiency.

[0175] 5) By comparing example 2, 5-6, 28-29, it can be seen that the D50 particle size of the nano-lubricating factor also affects the compaction density of the negative electrode sheet. When the D50 particle size of the nano-lubricating factor is 300 nm, the compaction density of the negative electrode sheet is the highest. When the D50 particle size is reduced to 100 nm and 30 nm, the compaction density of the negative electrode sheet gradually decreases with the decrease of the particle size. When the D50 particle size is increased to 600 nm and 900 nm, the compaction density of the negative electrode sheet gradually decreases with the increase of the particle size.

[0176] 6) By comparing example 2, 7, 25-27, it can be seen that the D50 particle size of the hard carbon material also affects the compaction density of the negative electrode sheet. When the D50 particle size of the hard carbon material is 6 μm, the compaction density of the negative electrode sheet is the highest. When the D50 particle size of the hard carbon material is reduced to 3 μm and 2 μm, the compaction density of the negative electrode sheet gradually decreases with the decrease of the particle size. When the D50 particle size is increased to 10 μm and 12 μm, the compaction density of the negative electrode sheet gradually decreases with the increase of the particle size, and accordingly, the resistivity of the negative electrode sheet also increases.

[0177] 7) By comparing example 1 and comparative example 1, it can be seen that when no nano-lubricating factor is added, the porosity of the negative electrode sheet increases significantly and the resistivity of the negative electrode sheet increases significantly, and the compaction density of the negative electrode sheet decreases significantly.

[0178] The above examples are only used to illustrate the technical solutions of the present application, but not to limit them. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent replacements to some or all of the technical features. Such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the examples of the present application.

Claims

1. A negative electrode sheet, wherein, The negative electrode active material layer comprises a hard carbon material and a nano-lubricating factor; The nano-lubricating factor comprises a mixture of nano-oxide and nano-sulfide with a mass ratio of (1-3):1; The nano-oxide is selected from SiO2 and / or Al2O3, and the nano-sulfide is selected from MoS2.

2. The negative electrode sheet according to claim 1, wherein The D50 particle size of the nano-lubricating factor is 50-800 nm.

3. The negative electrode sheet according to claim 1 or 2, wherein The D50 particle size of the hard carbon material is 3-10 μm.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein The mass ratio of the hard carbon material to the nano-lubricating factor is 100:(0.1-10).

5. The negative electrode sheet according to any one of claims 1 to 4, wherein The negative electrode active material layer further comprises a conductive agent and / or a binder; The mass ratio of the hard carbon material, the nano-lubricating factor, the conductive agent and the binder is (80-100):(1-5):(0-5):(0.1-10).

6. The negative electrode sheet according to any one of claims 1 to 5, wherein The compacted density of the negative electrode sheet is ≥ 0.98 g / cm 3 , the resistivity is 0.2-0.8 mΩ·cm, and the porosity is 30%-40%.

7. A battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1-6.

8. The battery of claim 7, wherein, The electrolyte comprises 5%-20% of NaPF6, 30%-60% of propylene carbonate, 30%-50% of ethyl methyl carbonate, 2%-5% of fluoroethylene carbonate, 0.1%-0.8% of propylene-1,3-sulfonic acid lactone and 0.2%-0.8% of vinyl sulfate, in terms of mass percentage.

9. The battery of claim 7 or 8, wherein, The injection coefficient of the electrolyte is 3-10 g / Ah. The test method of the injection coefficient is as follows: a fresh battery cell is weighed and recorded as the total weight g1; after the battery cell is disassembled, the weight of the dry electrode sheet g2 and the weight of the structural part g3 are measured, so as to obtain the injection amount g=g1-g2-g3; then the injection coefficient is calculated by the injection amount / battery capacity, and the unit is g / Ah.

10. An electronic device, comprising: The battery comprises the battery cell according to any one of claims 7-9.

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